Every day on his commute back home to Lincoln, Massachusetts, middle-aged MIT professor Walter Mason sees an earless woman take the same 5:22 p.m. train as him. The earless woman floods Walter’s imagination. The two never speak; they simply nod to each other across the station platform before boarding. When the woman fails to show up on the platform for several days, Walter begins to worry, preoccupying himself at work while wondering about the woman’s whereabouts. Her absence begins to disorient Walter. When the regular conductor on Walter’s train is substituted one day by a new conductor who informs Walter that his usual stop has been discontinued, Walter struggles to cope with the sudden changes in his daily life. The next day, however, the old conductor returns and tells Walter his absence was due to a day of conductor training. Additionally, Walter’s stop is not discontinued, after all. Moreover, the earless woman returns to the train with an ear implant. Order is restored to Walter's day, but Walter decides for once to take the train beyond his usual stop and venture further down the line.